# curs_color 3x

    curs_color(3x)                                           curs_color(3x)

## NAME

           start_color, init_pair, init_color, has_colors,
           can_change_color, color_content, pair_content, COLOR_PAIR
           - curses color manipulation routines

## SYNOPSIS

           # include <curses.h>
           int start_color(void);
           int init_pair(short pair, short f, short b);
           int init_color(short color, short r, short g, short b);
           bool has_colors(void);
           bool can_change_color(void);
           int  color_content(short  color, short *r, short *g, short
           *b);
           int pair_content(short pair, short *f, short *b);

## DESCRIPTION

       Overview
           curses support color attributes on terminals with that ca-
           pability.   To  use  these  routines  start_color  must be
           called, usually right after initscr.   Colors  are  always
           used  in pairs (referred to as color-pairs).  A color-pair
           consists of a foreground  color  (for  characters)  and  a
           background color (for the blank field on which the charac-
           ters are displayed).  A programmer  initializes  a  color-
           pair  with  the routine init_pair.  After it has been ini-
           tialized, COLOR_PAIR(n), a macro  defined  in  <curses.h>,
           can be used as a new video attribute.

           If  a  terminal  is capable of redefining colors, the pro-
           grammer can use the routine init_color to change the defi-
           nition   of   a   color.    The  routines  has_colors  and
           can_change_color  return  TRUE  or  FALSE,  depending   on
           whether  the  terminal  has color capabilities and whether
           the programmer can change the colors.   The  routine  col-
           or_content  allows  a programmer to extract the amounts of
           red, green, and blue components in an  initialized  color.
           The  routine  pair_content allows a programmer to find out
           how a given color-pair is currently defined.

       Routine Descriptions
           The start_color routine requires no arguments.  It must be
           called  if  the programmer wants to use colors, and before
           any other color manipulation routine  is  called.   It  is
           good  practice  to  call this routine right after initscr.
           start_color initializes eight basic  colors  (black,  red,
           green,  yellow,  blue,  magenta, cyan, and white), and two
           global variables,  COLORS  and  COLOR_PAIRS  (respectively
           defining  the maximum number of colors and color-pairs the
           terminal can support).  It also restores the colors on the
           terminal to the values they had when the terminal was just
           turned on.

           The init_pair routine changes the definition of  a  color-
           pair.   It takes three arguments: the number of the color-
           pair to be changed, the foreground color number,  and  the
           background color number.  For portable applications:

           -    The value of the first argument must be between 1 and
                COLOR_PAIRS-1.

           -    The value of the second and third arguments  must  be
                between  0 and COLORS.  Color pair 0 is assumed to be
                white on black, but is actually whatever the terminal
                implements before color is initialized.  It cannot be
                modified by the application.

           If the color-pair was previously initialized,  the  screen
           is  refreshed  and  all occurrences of that color-pair are
           changed to the new definition.

           As an extension, ncurses allows you to set  color  pair  0
           via  the  assume_default_colors routine, or to specify the
           use of default colors (color number -1) if you  first  in-
           voke the use_default_colors routine.

           The  init_color routine changes the definition of a color.
           It takes four arguments: the number of  the  color  to  be
           changed  followed  by three RGB values (for the amounts of
           red, green, and blue components).  The value of the  first
           argument  must  be between 0 and COLORS.  (See the section
           Colors for the default color index.)   Each  of  the  last
           three  arguments must be a value between 0 and 1000.  When
           init_color is used, all occurrences of that color  on  the
           screen immediately change to the new definition.

           The  has_colors routine requires no arguments.  It returns
           TRUE if the terminal can manipulate colors; otherwise,  it
           returns FALSE.  This routine facilitates writing terminal-
           independent programs.  For example, a programmer  can  use
           it  to decide whether to use color or some other video at-
           tribute.

           The can_change_color routine requires  no  arguments.   It
           returns  TRUE  if  the  terminal  supports  colors and can
           change their definitions; other, it returns  FALSE.   This
           routine facilitates writing terminal-independent programs.

           The color_content routine gives programmers a way to  find
           the intensity of the red, green, and blue (RGB) components
           in a color.  It requires four arguments: the color number,
           and  three addresses of shorts for storing the information
           about the amounts of red, green, and  blue  components  in
           the  given color.  The value of the first argument must be
           between 0 and COLORS.  The values that are stored  at  the
           addresses  pointed  to by the last three arguments are be-
           tween 0 (no component) and 1000 (maximum amount of  compo-
           nent).

           The  pair_content  routine  allows programmers to find out
           what colors a given color-pair consists of.   It  requires
           three  arguments: the color-pair number, and two addresses
           of shorts for storing the foreground  and  the  background
           color  numbers.   The  value of the first argument must be
           between 1 and COLOR_PAIRS-1.  The values that  are  stored
           at  the addresses pointed to by the second and third argu-
           ments are between 0 and COLORS.

       Colors
           In <curses.h> the following macros are defined.  These are
           the  default colors.  curses also assumes that COLOR_BLACK
           is the default background color for all terminals.

                 COLOR_BLACK
                 COLOR_RED
                 COLOR_GREEN
                 COLOR_YELLOW
                 COLOR_BLUE
                 COLOR_MAGENTA
                 COLOR_CYAN
                 COLOR_WHITE

## RETURN VALUE

           The routines can_change_color()  and  has_colors()  return
           TRUE or FALSE.

           All other routines return the integer ERR upon failure and
           an OK (SVr4 specifies only "an integer  value  other  than
           ERR") upon successful completion.

           X/Open  defines  no error conditions.  This implementation
           will return ERR on attempts to use  color  values  outside
           the range 0 to COLORS-1 (except for the default colors ex-
           tension), or use color pairs outside the range 0  to  COL-
           OR_PAIR-1.  Color values used in init_color must be in the
           range 0 to 1000.  An error is returned from all  functions
           if the terminal has not been initialized.  An error is re-
           turned from  secondary  functions  such  as  init_pair  if
           start_color was not called.

                  init_color
                       returns an error if the terminal does not sup-
                       port  this  feature,  e.g.,  if  the  initial-
                       ize_color capability is absent from the termi-
                       nal description.

                  start_color
                       returns an error If the color table cannot  be
                       allocated.

## NOTES

           In  the  ncurses implementation, there is a separate color
           activation flag, color palette, color pairs table, and as-
           sociated  COLORS  and  COLOR_PAIRS counts for each screen;
           the start_color function only affects the current  screen.
           The SVr4/XSI interface is not really designed with this in
           mind, and historical  implementations  may  use  a  single
           shared color palette.

           Note that setting an implicit background color via a color
           pair affects only character cells that a  character  write
           operation  explicitly  touches.   To change the background
           color used when parts of a window are blanked  by  erasing
           or scrolling operations, see curs_bkgd(3x).

           Several  caveats  apply  on 386 and 486 machines with VGA-
           compatible graphics:

           -    COLOR_YELLOW is actually brown.  To get  yellow,  use
                COLOR_YELLOW combined with the A_BOLD attribute.

           -    The  A_BLINK  attribute  should  in  theory cause the
                background to go bright.  This often fails  to  work,
                and  even  some cards for which it mostly works (such
                as the Paradise and compatibles) do the  wrong  thing
                when you try to set a bright "yellow" background (you
                get a blinking yellow foreground instead).

           -    Color RGB values are not settable.

## PORTABILITY

           This implementation satisfies XSI Curses's  minimum  maxi-
           mums for COLORS and COLOR_PAIRS.

           The  init_pair  routine  accepts  negative values of fore-
           ground  and  background  color  to  support  the   use_de-
           fault_colors  extension, but only if that routine has been
           first invoked.

           The assumption that COLOR_BLACK is the default  background
           color  for  all  terminals  can  be modified using the as-
           sume_default_colors extension.

           This implementation checks the  pointers,  e.g.,  for  the
           values  returned  by  color_content  and pair_content, and
           will treat those as optional parameters when null.

## SEE ALSO

           curses(3x), curs_initscr(3x), curs_attr(3x),  default_col-
           ors(3x)

                                                             curs_color(3x)